- Volume 98, Issue 1, 1977

Summary: Spirillum lipoferum, an N2-fixing organism, was grown at constant concentrations of dissolved O2. When supplied with NH4 + aerobically, its doubling time was 1 h; when it fixed N2 microaerophilically, its doubling time was 5·5 to 7 h and the optimal P o2 for growth was 0·005 to 0·007 atm. At its optimal P o2 for growth on N2, S. lipofernum assimilated 8 to 10 mg nitrogen/g carbon substrate used; its efficiency was less at higher P O2 levels. Nitrogenase in cell-free extracts required Mg2+ and Mn2+, and the Fe-protein was activated by Rhodospirillum rubrum activating factor. The nitrogenase had an optimal pH of 7·1 to 7·4 and an apparent K m for acetylene of 0·0036 atm. Extracts of S. lipoferum lost their nitrogenase activity on storage at −18 °C, and activity was restored by adding purified Feprotein from other N2-fixing bacteria.

Summary: The influence of the DNA synthesis inhibitor, nalidixic acid, on the properties of synchronous cultures of selected Rhodopseudomonas palustris swarmer cells was examined. There was little alteration in the changes in morphology, extinction, volume distribution and leucine incorporation up to bud development, and photosynthetic membrane lamellae were still synthesized de novo in the bud. However, there was no subsequent division, or flagellum or holdfast synthesis. Instead cells elongated by continued outgrowth of the abortive bud. Since DNA synthesis was also inhibited, this suggested a dependence of cell division, and flagellum and holdfast synthesis, on the completion of chromosome replication. By addition or removal of nalidixic acid at various times in the cell cycle, periods were demonstrated when the organism was insensitive to the antibiotic indicating that there was a pre-synthetic and post-synthetic gap in the pattern of DNA synthesis in R. palustris swarmers.

Summary: The buoyant densities of Escherichia coli k12 were investigated by isopycnic centrifugation in gradients of colloidal silica (Ludox) and polyvinylpyrrolidone. Bacteria from an exponential culture in a defined medium supplemented with hydrolysed casein banded at densities between 1·060 and 1·115 g ml−1; the mean density was 1·081 g ml−1. At the higher densities, two populations of cells were present: smaller cells were approximately twice as numerous as, and half the modal volume of, the population of larger cells. A homogeneous population of cells of intermediate volume equilibrated in the least dense region of the density band. Synchronous cultures were established by inoculating cells selected from the most or least dense regions of the band into spent growth medium. The results are consistent with a fluctuation between maximal density at cell birth and division, and minimal density near the middle of the cell cycle. In synchronous cultures prepared by continuous-flow age selection, the first division occurred after a period that was significantly shorter than the length of subsequent cell cycles. Cells selected by this procedure were of similar mean density to those in the exponential culture but were more homogeneous with respect to size. The possibility that the smallest (and densest) cells in an exponential culture are retained in the rotor, and are thus excluded from the synchronous culture, is discussed.

Summary: Whole-organism methanolysates of bacterionemae contained mycolic acids in addition to other long-chain fatty acids. These mycolic acids were similar in general structure and overall size to those found in strains of Corynebacterium diphtheriae and Corynebacterium xerosis. The long-chain fatty acids of bacterionemae, mainly straight-chain saturated and unsaturated acids, were similar to those of certain coryneform bacteria including C. diphtheriae. On the basis of these lipid data, and results of earlier studies, we recommend that the genus Bacterionema be transferred from the family Actinomycetaceae to the Coryneform Group of Bacteria.